Absolute position encoding method and absolute position encoder

Abstract: An absolute signal detecting method and an absolute encoder according to the present invention load a n-bit positional signal (3) to a counting circuit (12) through rotating a code plate (1) at power ON, and can obtain an absolute encoder signal (12A) after this load through performing count up/down of the counting circuit (12) with an incremental signal (2).

Description: The present invention relates to an absolute position encoding method and an absolute position encoder, and more particularly, to a new improvement for obtaining an absolute position encoder in a structure almost similar to an incremental position encoder. Heretofore, a commonly used absolute position encoder, for example, one disclosed in Japanese Patent Laid-Open No. Hei 4-319621 uses one-track type of n-bit positional signals (well-known recurrent random number codes) to detect said n-bit positional signals through disposing n light receiving elements corresponding to the n bits toward the track (toward the circumference), and output the n-bit positional signals as positional signals accompanying displacement of an input axis position of the encoder. Since conventional encoders are composed as above described, there are following issues. The required number of signal processing circuits corresponding to the n elements that correspond to said n bits is n circuits. Problems such as signal adjustment of each of the n circuits exist due to variation in frequency characteristics between the n circuits, and hence it is very difficult to produce absolute encoders in high reliability. Electronics Letters, vol. 25, no. 21, page 1436/1437 XP 000080091 Ross J N et al "Incremental Digital Position Encoder with Error Detection and Correction" describes an arrangement having a n-bit pseudorandom binary sequence and an incremental code. The present invention aims to solve the above issues, and in particular, an object of the present invention is to obtain an absolute position encoding method and an absolute position encoder in a structure almost similar to an incremental position encoder. According to a first aspect of the present invention, there is provided an absolute position encoding method using a n-bit positional signal (3) formed on a first track (1b) of a code plate (1) and an incremental signal (2) having a pitch corresponding to that of said n-bit positional signal (3), formed on a second track (1a) of the code plate, said absolute position encoding method comprising the steps of: reading said n-bit positional signal (3) at the time of turning power ON and loading said n-bit positional signal into a counting circuit (12); and detecting the input axis position through performing count up/down of said counting circuit (12) in response to said incremental signal (2); characterised by detecting the frequency of said incremental signal, and not loading said counting circuit when the rotation speed of the input axis is over a predetermined value; and by using a latch circuit (10) to read said n-bit signal (3) at the instants when said incremental signal changes its value. In a refinement this method further comprises loading said read n-bit signal through a serial to parallel signal converter into said counting circuit. In a further refinement, when the load of said n-bit positional signal to said counting circuit is completed, the load command circuit outputs a load completion signal. According to a second aspect of the present invention, there is provided an absolute position encoder which determines an absolute position signal (12A) using a n-bit positional signal (3) formed on a first track (1b) of a code plate (1) and an incremental signal (2) having a pitch corresponding to that of said n-bit positional signal (3) formed on a second track (1a) of the code plate, said absolute position encoder comprising an UP/DOWN circuit (11) where said incremental signal (2) is inputted, a counting circuit (12) connected to said UP/DOWN circuit (11) whereby said n-bit positional signal (3) is read at the time of turning power ON and loaded into the counting circuit, a latch circuit (10) where said n-bit positional signal (3) and said incremental signal are inputted, a serial to parallel signal converter (13) connected to said latch circuit (10) and said counting circuit (12), and a load command circuit (14) connected to said serial to parallel signal converter (13) and counting circuit (12), characterised by a load command circuit (14) for said n-bit positional signal (3) which detects the frequency of said incremental signal (2), and does not issue a load command to said counting circuit (12) when the rotation speed of the input axis is over a predetermined value. In further detail, between said serial to parallel signal converter and counting circuit, a pure binary signal converter is provided. An absolute position encoding method and an absolute position encoder according to the present invention rotate a code plate having a randomized-type of n-bit positional signal formed at one track, detect this n-bit positional signal with two light receiving elements for a n-bit signal and a n -bit signal, and scan each bit of this n-bit positional signal with a latch circuit by a leading edge (a trailing edge is also possible) that is a changing point of an incremental signal corresponding to this n-bit signal. The n-bit positional signal detected with this scanning is stored as a parallel signal per bit in a counting circuit through a serial to parallel signal converter from the latch circuit, and preparation is completed. It is possible to obtain an absolute signal through inputting to the counting circuit the result of addition/subtraction corresponding to the upward/downward value of the incremental signal generated with rotation of the code plate on the basis of the n-bit positional signal stored in said counting circuit. In addition, the light receiving element for the n -bit signal is used for compensation of lack of light quantity of the n-bit positional signal, and in the present invention, above described operations can be obtained with only the light receiving element for the n-bit signal. Figure 1 is a structural diagram showing an absolute encoder according to the present invention. Hereafter, preferable embodiments of an absolute position encoding method and an absolute position encoder according to the present invention will be explained in detail with drawings. A code plate is shown by reference numeral 1 in Figure 1, and the code plate has a first track 1a with a code for a known incremental signal 2, a second track 1b with a code for a n-bit positional signal 3 (composed of well-known recurrent random number codes), and is provided in free rotation. To the left of this code plate 1 in Figure 1, a first light source 4, and a second light source 5 corresponding to respective tracks 1a and 1b are provided individually. A light receiving section 6 for an incremental position signal, and a light receiving section 7 for an absolute position signal corresponding to said respective tracks 1a and 1b are provided, and this light receiving section 7 for an absolute position signal is composed of a first light receiving section 7a to output a n-bit positional signal 3 and a second light receiving section 7b to output a n -bit positional signal 3A. Said incremental signal 2 and n-bit positional signal 3 are inputted to the latch circuit 10, and the incremental signal 2 is also inputted to an UP/DOWN circuit 11 connected to a counting circuit 12. Said latch circuit 10 is connected to a parallel signal converter 13 for conversion of a serial signal to a parallel signal, which is connected to said counting circuit 12 through a pure binary signal converter 100. A load command circuit 14 connected to a pure binary signal converter 100 is connected to said counting circuit 12 and a load command latch circuit 101, and load (storage) to the counting circuit 12 is started with a load command signal 14a from this load command circuit 14. In addition, the incremental signal 2 is inputted to the load command circuit 14 through a frequency comparator 102, and only when the incremental signal 2 indicates, for example, that a rotary encoder is rotating at the speed less than or equal to 300 RPM, the load command signal 14a is issued. Next, operations will be described. At first, this embodiment rotates the code plate 1 (for example, if the axis position is 100/360°, the number, 100 becomes the absolute value) through operating an absolute position encoder connected to a robot and the like so as to load (store as an initial value) a n-bit positional signal 3 in a parallel mode to a counting circuit 12, inputs to a latch circuit 10 the n-bit positional signal 3 in a random mode (for example, 0001) from the first light receiving section 7a of a light receiving section 7 for an absolute signal by the second track 1b of the code plate 1, and inputs also an incremental signal 2 in the same pitch corresponding to the pitch of this n-bit positional signal 3 to this latch circuit 10. In this latch circuit 10, this embodiment scans each bit of this n-bit positional signal 3 with a leading edge (a trailing edge is also possible) that is a changing point of the incremental signal 2, converts the n-bit positional signal 10A in a serial mode detected at this scanning to a parallel signal in the serial to parallel signal converter 13 and the pure binary signal converter 100, and stores the n-bit positional signal as an absolute value in the counting circuit 12 that starts load with a load command signal 14a. Therefore, storage of this n-bit positional signal 3 derived from the codes of the second track of the rotated code plate 1 is completed. At the time of this load completion to the counting circuit 12, a load completion signal 101A is issued. In addition, this frequency comparator 102 compares a rotation speed to the regular value so as to perform the load only when the rotation speed of the encoder is, for example, less than or equal to 300 RPM. Next, in case this absolute encoder is used, the up/down direction of the incremental signal 2 generated with rotation of the code plate of an input axis (not shown) is detected with the UP/DOWN circuit, an UP signal 1 la or a DOWN signal 11b are inputted to the counting circuit 12, and this calculation result is outputted as an absolute encoder signal 12A of the input axis position in the upward or downward mode through adding this incremental signal 2 in either direction to this n-bit positional signal 3 that is the absolute value. Therefore, since the signal processing system for processing the n-bit positional signal 3 becomes one circuit, it is not necessary to use n channels of signal processing systems as conventional. Since an absolute position encoding method and an absolute position encoder according to the present invention are composed of as above described, following effects can be obtained. Thus, since as a n-bit processing system, the series number changes from the conventional n channels to one circuit, drastic hardware reduction can be attained. Furthermore, since the frequency characteristic of the incremental signal is better than that of the n-bit positional signal due to detection in larger received-light quantity with a plurality of slits, the absolute signal in good frequency characteristic can be obtained. Still more, after completion of load to the counting circuit, the absolute value can be obtained from only the incremental signal through having operated the counting circuit with the incremental signal.

Claims: An absolute position encoding method using a n-bit positional signal (3) formed on a first track (1b) of a code plate (1) and an incremental signal (2) having a pitch corresponding to that of said n-bit positional signal (3), formed on a second track (1a) of the code plate, said absolute position encoding method comprising the steps of: reading said n-bit positional signal (3) at the time of turning power ON and loading said n-bit positional signal (3) into a counting circuit (12); and detecting an input axis position through performing count up/down of said counting circuit (12) in response to said incremental signal (2); characterised by detecting the frequency of said incremental signal, and not loading said counting circuit when the rotation speed of the input axis is over a predetermined value ; and by using a latch circuit (10) to read said n-bit signal (3) at the instants when said incremental signal changes its value. An absolute position encoding method as claimed in claim 1, further comprising loading said read n-bit positional signal (3) through a serial to parallel signal converter (13) into said counting circuit (12). An absolute position encoding method as claimed in claim 1 or claim 2, whereby, when the load of said n-bit positional signal (3) into said counting circuit (12) is completed, a load completion signal is outputted. An absolute position encoder which determines an absolute position signal (12A) using a n-bit positional signal (3) formed on a first track (1b) of a code plate (1) and an incremental signal (2) having a pitch corresponding to that of said n-bit positional signal (3) formed on a second track (1a) of the code plate, said absolute position encoder comprising an UP/DOWN circuit (11) where said incremental signal (2) is inputted, a counting circuit (12) connected to said UP/DOWN circuit (11) whereby said n-bit positional signal (3) is read at the time of turning power ON and loaded into the couting circuit, a latch circuit (10) where said n-bit positional signal (3) and said incremental signal (2) are inputted, a serial to parallel signal converter (13) connected to said latch circuit (10) and said counting circuit (12), and a load command circuit (14) connected to said serial to parallel signal converter (13) and counting circuit (12), characterised by a load command circuit (14) for said n-bit positional signal (3) which detects the frequency of said incremental signal (2), and does not issue a load command to said counting circuit (12) when the rotation speed of the input axis is over a predetermined value. An absolute position encoder as claimed in claim 4, wherein between said serial to parallel signal converter (13) and the counting circuit (12), a pure binary signal converter (100) is provided.

Inventors: SEKI SHIGEO, SEKI, SHIGEO, SEKI, SHIGEO C/O TAMAGAWA SEIKI K.K.
Applicants: TAMAGAWA SEIKI CO LTD, TAMAGAWA SEIKI KABUSHIKI KAISHA
Application year: 1994
Main classification: H03M1
IPC codes: G01D5, H03M1